Chimps may be portrayed as mischieviously fun but largely harmless by Hollywood, but the truth is anything but. In the wild, chimpanzees are killers that engage in years-long war against one another, and their behavior may explain man's propensity for violence:

It was a four-year "war" witnessed by Dr Jane Goodall, and Dr Muller's PhD supervisor, Richard Wrangham, a professor of primatology from Harvard University, Boston, that put an end to our cosy ideas.

In the Seventies, Prof Wrangham and Dr Goodall watched a group of chimpanzees split into two factions. One group killed every male and some of the females in the other group. The victims had recently been their companions.

Although Dr Goodall was the first to suggest it, Prof Wrangham went on to develop a theory that would explain human violence based on the aggression he had witnessed. As he points out, we are hardly a peaceful species. In Britain, men are 24 times more likely to kill or assault another person, and 263 times more likely to commit a sexual offence than a woman.

Prof Wrangham's theory is called the Demonic Male Hypothesis. He argues that human males and chimps share a tendency to be aggressive with our closest common ancestor. Chimpanzees and humans have many attributes in common: we share approximately 98.5 per cent of our DNA, we both hunt and males show a strong desire to form alliances against other males while jockeying for status. Male chimpanzees are hostile towards other groups of chimps; you don't even have to go to Arsenal to know that men are not dissimilar.